Millimeter wave signals are used for radar and telecommunications. They are also capable of being used to produce an image of a subject by directing millimeter-wave signals at the subject and detecting the reflected signal. Examples of such imaging systems are described in U.S. Pat. Nos. 5,455,590; 5,557,283; 5,859,609; and 6,507,309; U.S. patent application Ser. No. 10/607,552 filed Jun. 26, 2003; U.S. patent application Ser. No. 10/697,848 filed Oct. 30, 2003; U.S. patent application Ser. No. 10/301,522 filed Nov. 21, 2002; and U.S. patent application Ser. No. 10/697,965 filed Oct. 30, 2003, which patent references are incorporated herein by reference.
Imaging systems, as described above provide relatively detailed images of a subject, including a person's body and any objects carried by the person, whether or not the objects are concealed. An operator can view images of a subject and visually identify objects included with the person. Other detection devices can also be used to obtain other information about a subject. For instance, the subject can pass through a metal detector to determine if the subject has a detectable metal object. When the surveillance system is part of a process of boarding a public transportation vehicle, or entering a public or protected facility, substantial delays may be realized. Further, the effectiveness of the surveillance depends on the accuracy and attentiveness of the operator or operators.